The present invention relates to memory devices generally and, more particularly, to a memory device that transfers a fixed number of words of data with each access.
A synchronous Static Random Access Memory (SRAM) can provide data from multiple address locations using a single address. Accessing multiple locations in response to a single address is called a burst mode access. A memory device that provides a burst mode can reduce activity on the address and control buses. The burst mode of a conventional synchronous SRAM can be started and stopped in response to a control signal.
A conventional Dynamic Random Access Memory (DRAM) preserves data during periodic absences of power by implementing a memory cell as a capacitor and an access transistor. Since the charge on the capacitor will slowly leak away, the cells need to be xe2x80x9crefreshedxe2x80x9d once every few milliseconds. Depending on the frequency of accesses, a conventional DRAM can need an interrupt to perform data refreshes. Using a DRAM in a burst application is difficult because of the need to refresh. Completely hiding refresh cycles (e.g., refreshing data without the need for interrupts) in a DRAM cannot happen with conventional memory devices due to architecture choices that have been made. Data word bursts can be interrupted while in progress since conventional architectures support both burst and single access modes. Conventional DRAM access takes about 10 ns to get data, but nearly 20 ns to complete writeback and equalization. The addition of another 20 ns for a refresh results in a total access of 40 ns.
Since the data burst transfers of conventional memories can be interrupted and single accesses made, the amount of time that the data, address and control busses are not in use can vary. The variability of bus availability complicates the design of systems with shared data, address and control busses.
It would be desirable to have a memory device that has a fixed burst length.
The present invention concerns an integrated circuit comprising a memory and a logic circuit. The memory may comprise a plurality of storage elements each configured to read and write data in response to an internal address signal. The logic circuit may be configured to generate a predetermined number of the internal address signals in response to (i) an external address signal, (ii) a clock signal and (iii) one or more control signals. The generation of the predetermined number of internal address signals may be non-interruptible.
The objects, features and advantages of the present invention include providing a fixed burst memory that may (i) give network customers who typically burst large data lengths the ability to set a fixed burst length that suits particular needs; (ii) have non-interruptible bursts; (iii) free up the address bus and control bus for a number of cycles; (iv) provide programmability for setting the burst length by using DC levels [Vss or Vcc] on external pins; (v) hide required DRAM refreshes inside a known fixed burst length of data words; and/or (vi) operate at higher frequencies without needing interrupts to perform refreshes of data.